database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-11-26 23:43:30 +03:00
Code Activity

Don't force-assign transaction id when exporting a snapshot.

Browse Source 
Previously we required every exported transaction to have an xid
assigned. That was used to check that the exporting transaction is
still running, which in turn is needed to guarantee that that
necessary rows haven't been removed in between exporting and importing
the snapshot.

The exported xid caused unnecessary problems with logical decoding,
because slot creation has to wait for all concurrent xid to finish,
which in turn serializes concurrent slot creation.   It also
prohibited snapshots to be exported on hot-standby replicas.

Instead export the virtual transactionid, which avoids the unnecessary
serialization and the inability to export snapshots on standbys. This
changes the file name of the exported snapshot, but since we never
documented what that one means, that seems ok.

Author: Petr Jelinek, slightly editorialized by me
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/f598b4b8-8cd7-0d54-0939-adda763d8c34@2ndquadrant.com
This commit is contained in:
Andres Freund
2017-06-14 11:57:21 -07:00
parent b6966d4627
commit 6c2003f8a1
7 changed files with 115 additions and 67 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
src/backend/storage/ipc/procarray.c
View File

@@ -1793,14 +1793,15 @@ GetSnapshotData(Snapshot snapshot)
* Returns TRUE if successful, FALSE if source xact is no longer running.
*/
bool
ProcArrayInstallImportedXmin(TransactionId xmin, TransactionId sourcexid)
ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid)
{
bool result = false;
ProcArrayStruct *arrayP = procArray;
int index;
Assert(TransactionIdIsNormal(xmin));
if (!TransactionIdIsNormal(sourcexid))
if (!sourcevxid)
return false;
/* Get lock so source xact can't end while we're doing this */
@@ -1817,8 +1818,10 @@ ProcArrayInstallImportedXmin(TransactionId xmin, TransactionId sourcexid)
if (pgxact->vacuumFlags & PROC_IN_VACUUM)
continue;
xid = pgxact->xid; /* fetch just once */
if (xid != sourcexid)
/* We are only interested in the specific virtual transaction. */
if (proc->backendId != sourcevxid->backendId)
continue;
if (proc->lxid != sourcevxid->localTransactionId)
continue;
/*

26
src/backend/storage/lmgr/predicate.c
View File

@@ -148,7 +148,7 @@
* predicate lock maintenance
* GetSerializableTransactionSnapshot(Snapshot snapshot)
* SetSerializableTransactionSnapshot(Snapshot snapshot,
* TransactionId sourcexid)
* VirtualTransactionId *sourcevxid)
* RegisterPredicateLockingXid(void)
* PredicateLockRelation(Relation relation, Snapshot snapshot)
* PredicateLockPage(Relation relation, BlockNumber blkno,
@@ -434,7 +434,8 @@ static uint32 predicatelock_hash(const void *key, Size keysize);
static void SummarizeOldestCommittedSxact(void);
static Snapshot GetSafeSnapshot(Snapshot snapshot);
static Snapshot GetSerializableTransactionSnapshotInt(Snapshot snapshot,
TransactionId sourcexid);
VirtualTransactionId *sourcevxid,
int sourcepid);
static bool PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag);
static bool GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag,
PREDICATELOCKTARGETTAG *parent);
@@ -1510,7 +1511,7 @@ GetSafeSnapshot(Snapshot origSnapshot)
* one passed to it, but we avoid assuming that here.
*/
snapshot = GetSerializableTransactionSnapshotInt(origSnapshot,
InvalidTransactionId);
NULL, InvalidPid);
if (MySerializableXact == InvalidSerializableXact)
return snapshot; /* no concurrent r/w xacts; it's safe */
@@ -1643,7 +1644,7 @@ GetSerializableTransactionSnapshot(Snapshot snapshot)
return GetSafeSnapshot(snapshot);
return GetSerializableTransactionSnapshotInt(snapshot,
InvalidTransactionId);
NULL, InvalidPid);
}
/*
@@ -1658,7 +1659,8 @@ GetSerializableTransactionSnapshot(Snapshot snapshot)
*/
void
SetSerializableTransactionSnapshot(Snapshot snapshot,
TransactionId sourcexid)
VirtualTransactionId *sourcevxid,
int sourcepid)
{
Assert(IsolationIsSerializable());
@@ -1673,7 +1675,8 @@ SetSerializableTransactionSnapshot(Snapshot snapshot,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("a snapshot-importing transaction must not be READ ONLY DEFERRABLE")));
(void) GetSerializableTransactionSnapshotInt(snapshot, sourcexid);
(void) GetSerializableTransactionSnapshotInt(snapshot, sourcevxid,
sourcepid);
}
/*
@@ -1687,7 +1690,8 @@ SetSerializableTransactionSnapshot(Snapshot snapshot,
*/
static Snapshot
GetSerializableTransactionSnapshotInt(Snapshot snapshot,
TransactionId sourcexid)
VirtualTransactionId *sourcevxid,
int sourcepid)
{
PGPROC *proc;
VirtualTransactionId vxid;
@@ -1741,17 +1745,17 @@ GetSerializableTransactionSnapshotInt(Snapshot snapshot,
} while (!sxact);
/* Get the snapshot, or check that it's safe to use */
if (!TransactionIdIsValid(sourcexid))
if (!sourcevxid)
snapshot = GetSnapshotData(snapshot);
else if (!ProcArrayInstallImportedXmin(snapshot->xmin, sourcexid))
else if (!ProcArrayInstallImportedXmin(snapshot->xmin, sourcevxid))
{
ReleasePredXact(sxact);
LWLockRelease(SerializableXactHashLock);
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("could not import the requested snapshot"),
errdetail("The source transaction %u is not running anymore.",
sourcexid)));
errdetail("The source process with pid %d is not running anymore.",
sourcepid)));
}
/*